An important goal of nondestructive evaluation is the detection and classification of flaws in materials. This process of 'flaw classification' involves the transformation of the 'raw' data into other domains, the extraction of features in those domains, and the use of those features in a classification algorithm that determines the class to which the flaw belongs.

In this work, we describe a flaw classification software system, CLASS and the updates made to it. Both a hierarchical clustering algorithm and a backpropagation neural network algorithm were implemented -and integrated with CLASS. A fast Fourier transform routine was also added to CLASS in order to enable the use of frequency domain and cepstral domain features.

This extended version of CLASS is a very user friendly software, which requires the user to have little knowledge of the actual learning algorithms. CLASS can be easily extended further, if needed, in the future.

The layup sequence in a composite laminate greatly effects its properties. If one ply is misaligned in the layup sequence, it can result in the part being rejected and discarded. At the present time, most manufacturers cut a small coupon from the waste edge and use a microscope to optically verify the ply orientations on critical parts. This can add a substantial cost to the product since the test is both labor intensive and performed after the part is cured. A nondestructive teclmique which could be used to test the part after curing and require less time than the optical test would be very beneficial, and one that could be performed prior to curing would be extremely desirable. Preliminary tests demonstrate a high probability that the model and tests developed in this thesis can be used for characterizing uncured layups as well.

The aerospace industry, driven by a demand to reduce weight, has relied increasingly on composite materials to increase performance of advanced systems. However, impacts by foreign objects such as runway debris can damage composite components without leaving indentations or other visually identifiable marks. Microcracking of the matrix, fiber pullout, and delaminations are among the types of resultant internal damage that can weaken the structure and affect the ultimate load strength as well as fatigue life. The field of nondestructive evaluation (NDE) provides a means for the detection and evaluation of barely visible impact damage. In this study glass/epoxy, carbon/epoxy, and carbon/thermoplastic material systems were evaluated ultrasonically after being struck at low impact energy levels. Laminates were impacted following NASA specifications; two different clamped impact boundaries were evaluated. Impact energies were varied by adjusting the drop height or the mass of the impactor. Impact events were recorded with a video camera and the energetics were obtained from the video tape; these included the incident and rebound energy and velocity. The energy dissipated in the laminate as a consequence of the impact can therefore be determined. The total delamination area, as summed over all the ply interfaces through the thickness of the laminate, was determined from ultrasonic scans and then quantitatively correlated to the energy dissipated in the laminate. A destructive deplying technique was applied to woven laminates to obtain the size and morphology of the impact delaminations. These results were compared to NDE results. The ability of delaminations to block ultrasound and the resulting shadowing effects were investigated. Finally, the impact resistance of a thermoset system (carbon/epoxy) and a thermoplastic system (carbon/PPS) were compared and no significant difference was found.

Reducing the noise radiated by internal combustion engine and electric powered rotary lawn mowers is becoming a topic of great concern among many members of the Outdoor Power Equipment Industry (OPEl). This concern has been fueled by a comprehensive legislative directive designed to limit the noise levels of outdoor power equipment sold to member states of the European Union (EU) has recently been issued. This directive will have a dramatic effect on the existing trade markets of both European and U.S. manufacturers and pose entry barriers for new markets because these limitations are believed to be beyond the present technical capabilities that OPEl members are willing to develop for production lawn mowers.

Over the past forty years, the problem of nonspecular reflection of bounded beams from fluid-solid interfaces has been studied extensively. Early studies by Schoch and Bertoni and Tamir have concentrated on planar structures, both halfspaces and plates. More recent studies of reflection of sound from cylinders have concentrated on effectively planar incident fields, where the sound wave field does not vary appreciably over the cylinder diameter.

The problem discussed here, nonspecular Gaussian beam reflection from cylindrical shells, differs from the previous studies in that the incident field has a substantial spatial variation over the cylinder radius. Zeroug and Felsen studied the theoretical aspects of nonspecular reflection of divergent and collimated beams from planar and cylindrical interfaces. In their analysis, the plane interface results were extended to the cylindrical case by mapping the problem geometry to cylindrical coordinates 'k and solving in terms of cylinder functions, while assuming locally planar conditions.

http://www.worldcat.org/oclc/22939799

http://www.worldcat.org/oclc/32804161

http://www.worldcat.org/oclc/37760275